build: switch source archive to xz compression

And a few minor README improvements

Change-Id: I667860f46b19d1ec885fd81910a116581007ac8f
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e5cc01a..ae09443 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -3,7 +3,7 @@
   push:
     paths-ignore:
       - 'docs/**'
-      - '*.conf.sample'
+      - '*.conf.sample*'
       - '*.md'
       - '.mailmap'
   workflow_dispatch: